Obtaining film uniformity in substrate processing can be difficult when there is an uneven distribution of gas applied to substrates. The uneven distribution of gas may cause uneven growth of film or crystalline instability, among other issues. This may cause defects in the finished products, and thus, may render them unusable.
The uneven distribution of gas may be attributable to the way flows occur in a reaction system. A single source of gas may provide a required precursor along many points of a substrate's surface. But a distance traveled by gas at one point of the substrate's surface may differ than that of another location on the substrate's surface. This may be due to the unequal length lines of a gas distribution system.
FIG. 1 shows a prior art gas distribution system 100 for depositing an epitaxial film on a substrate. The gas distribution system 100 may include a base gas source (not pictured) that provides a base gas to a base gas feed 102. The base gas feed 102 may include a gas line and fittings. An example of the gas line in the gas distribution system 100 may be a high purity gas line (316L SST, electro-polished inside) manufactured by Swagelok®.
The base gas may then pass through base gas feed 102 to a base gas distribution rail 104, which extends across the substrate's surface. From the base gas distribution rail 104, the base gas then passes downward through an upper base gas feed line 106 to a metering or proportioning valve 108, of which seven of both the upper base gas feed line 106 and the metering or proportioning valve 108 are shown in FIG. 1. The metering or proportioning valve 108 may control a flow rate of the base gas to a lower base gas feed line 110. The metering or proportioning valve 108 may comprise a Swagelok® BM-series High-purity metering valve.
From the lower base gas feed line 110, the base gas may reach a gas injection port 112. The gas injection port 112 may be coupled an injection flange 114, which is installed onto a chamber 116. The base gas may then enter into the chamber 116 and encounter a substrate to be processed.
The gas distribution system 100 may also include a dopant gas source that provides a dopant gas to a dopant gas feed 118. Similar to the base gas feed 102, the dopant gas feed 118 may also include a gas line and fittings. The dopant gas may then pass through to a dopant gas distribution rail 120 and then an upper dopant gas feed line 122.
The dopant gas then proceeds from the upper dopant gas feed line 122 to a metering or proportioning valve 124, of which three are shown in FIG. 1. The metering or proportioning valve 124 may control a flow rate of the dopant gas to a lower dopant gas feed line 126.
From the lower dopant gas feed line 126, the dopant gas may reach a dopant injection port 128. The dopant injection port 128 may be coupled an injection flange 114, which is installed onto a chamber 116. The dopant gas may then enter into the chamber 116 and encounter a substrate to be processed.
As shown in FIG. 1, a distance traveled by a gas may differ based on which injection port the gas travels through. For example, a gas that enters an injection port centered in the middle of the substrate may travel much less than a gas that enters an injection port on the ends of the substrate. Such may be reflected in the lengths of the lower base gas feed line 110 and the lower dopant gas feed line 126.
The difference in distance traveled may reflect themselves in the flow rates of gas, and the pressures within the gas lines. FIG. 2 illustrates a pressure diagram of a prior art gas distribution system. The pressure diagram reflects a greater pressure difference for gas lines 130 located in the middle of the substrate compared to gas lines 132 located on the ends of the substrate. With a greater pressure difference, a higher flow rate is possible for the gas lines 130 in comparison to gas lines 132. Such may result in more deposition occurring in the middle of the substrate compared to the edges.
As a result, a need exists for a system that distributes gas in a manner that improves film uniformity.